Chemical-thermal cleaning techniques

Consequently, the advantages of the chemical-thermal cleaning technique using chlorine trifluoride are summarized as follows ... 

Heat transfer surface cleaning techniques can be applied either online or off-line. Online techniques (usually used for tubeside applications) include various mechanical techniques (flow-driven or power-driven rotating brushes, acoustic/mechanical vibration, chemical feeds, flow reversal, etc.). Off-line techniques include chemical cleaning, mechanical cleaning by circulating particulate slurry, and thermal baking to melt frost/ice deposits. 

Some of these techniques using electrons and photons as probes of the surface chemistry have been described in this symposium by other authors. In this paper methods of surface analyses using beams of ions will be described. Emphasis is placed on ion scattering spectrometry (ISS) and secondary ion mass spectrometry (SIMS). Examples are shown for adhesive bonding applications including determination of locus of failure, contamination, cleaning and thermal and chemical pretreatments. 

One-electron oxidation of phenyl iron(III) tetraarylpor-phyrin complexes with bromine in chloroform at —60°C produces deep red solutions whose H and H NMR spectra indicate that they are the corresponding iron(IV) complexes. For the low-spin aryl Fe porphyrins the electron configuration is (dxyf(dxz,dyzf, with one tt-symmetry unpaired electron, and for the low-spin aryl Fe porphyrins the electron configuration is d, yf- d, zAyzf with two TT-symmetry unpaired electrons. The aryl Fe porphyrins are thermally unstable, and upon warming convert cleanly to A-phenylporphyrin complexes of Fe by reductive elimination. This process has been investigated by electrochemical techniques, by which it was shown that the reversible (at fast scan rates) one-electron oxidation of a-aryl complexes of PFe was followed by an irreversible chemical reaction that yielded the Fe complex of the A-phenylporphyrin, which could then be oxidized reversibly by one electron to yield the Fe complex of the A-phenylporphyrin. (If the Fe complex of the N-phenylporphyrin is instead reduced by one electron, the Fe complex of the A-phenylporphyrin is formed reversibly at... 

Thermal desorption from a solid phase microextraction (SPME) fiber has shown considerable potential for selectively introducing semivolatile chemicals into an IMS. ° The SPME approach is a simple design patterned after the early platinum wire introduction thermal desorption system described. With SPME, semivolatile compounds are extracted by either absorption or adsorption onto a nonvolatile polymeric coating or solid sorbent phase that has been coated onto a small fiber. Normally, the adsorption liber is housed in the needle of a syringe to permit puncture of a sample bottle septum and to protect the fiber from contamination during transfer of the fiber from the sample to the IMS instrument. After the analytes are adsorbed onto the SPME fiber, the fiber is retracted into the needle and then injected in a normal syringe technique such that the fiber is extended into the heated region of the IMS and the analytes are desorbed from the fiber into the clean carrier gas of the IMS. 

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